1. Field of the Invention
The present invention relates to hoists and more particularly to hoists including a backbone and a rotating, cable-wound drum.
2. Description of the Related Art
One conventional type of hoist includes a cable that is wound and unwound from a drum to move a load. An example of such a hoist is shown as hoist system 100 in FIG. 1. Hoist system 100 includes: building structure 102; hoist backbone 104; reducer connecting hardware set 105; motor 106; shaft 108; reducer assembly 110 (sometimes simply called, “the reducer”); cable 116; load 118; drum 120; and end bearing assembly 122. Co-ordinate axes set 101 shows the six degrees (or directions) of motion that various points in system 100 may have, including: (i) along X (that is, the direction into and out of the page); (ii) rotation about the X axis (or θX); (iii) along Y; (iv) rotation about the Y axis (or θY); (v) along Z; and (vi) rotation about the Z axis (or θZ). The reducer includes first bearing 112 and second bearing 114. The end bearing assembly includes third bearing 124. The shaft is constrained by the first, second and third bearings so that it is free to rotate in the θZ direction. The motor selectively drives, through the reducer, rotation of the shaft so that the cable is selectively wound and unwound to move the load through the cable.
In system 100: (i) the end bearing assembly (including the third bearing) is very rigidly and precisely located in space; (ii) the reducer (including the first and second bearings) is very rigidly and precisely located in space; and (iii) the shaft is made to be precisely co-axial with axis A1. Because of this precision and rigidity, the system works well. Unfortunately, it has been recognized that it is difficult to make all the components of system 100 so that they exhibit the precision and rigidity required for smooth operation. If there are variation from the above-noted types of precision and/or rigidity identified in this paragraph, then the shaft may be influenced to bend, as shown (in an exaggerated manner) by curved axis A2. If the shaft is bent, or stressed to bend by the bearings, in the bent direction of axis A2, then stresses and strains will cause, wear, damage and/or failure of the components of system 100. System 100 will not work well when the shaft is bent or stressed in the bending direction. As an example of the issues involved in giving system 100 the requisite degree of rigidity and precision, the backbone is precisely manufactured of very rigid material. As a further example of the issues involved in giving system 100 the requisite degree of rigidity and precision, reducer connecting hardware set 105 must rigidly and precisely connect the reducer, as well as bearings 112 and 114, to the backbone.
Because of the difficulty and/or expense in manufacturing hoist system components with the requisite degree of rigidity and/or precision, some conventional systems allow the bearings that constrain the shaft to have certain degrees (or directions) and quanta of freedom of motions. One conventional example, shown in FIG. 2, is shaft mounting hoist system 200. Hoist system 200 includes: building structure 202; hoist backbone 204; reducer connecting hardware set 205; motor 206; shaft 208; reducer 210 (sometimes simply called “the reducer”); cable 216; load 218; drum 220; end bearing assembly 222; and intermediate bearing assembly 224. Co-ordinate axes set 201 shows the six degrees (or directions) of motion that various points in system 200 may have. The reducer includes first bearing 212 and second bearing 214. The end bearing assembly includes third bearing 224. The intermediate bearing assembly includes pillow block bearing 228. The shaft is constrained by the first, second and third bearings so that it is free to rotate in the θZ direction. The motor selectively drives, through the reducer, rotation of the shaft so that the cable is selectively wound and unwound to move the load through the cable.
In shaft mounting hoist system 200, the reducer connecting hardware set connects the reducer assembly to the backbone so that degrees and freedom/constraint are determined with respect to a constraint point (see DEFINITIONS section). More specifically, the constraint point has the following degrees of freedom/constraint, relative to the backbone: (i) free in along X; (ii) free in rotation about X; (iii) fixed in along Y; (iv) free in rotation about Y; (v) free in along Z; and (vi) free in rotation about Z. In other words, the reducer connecting hardware set is further structured so that the constraint point is only rigidly constrained (relative to the backbone) in the along-Y direction, and this constraint point must be offset from the axis of rotation in the along-X direction. Alternatively, the sole direction of constraint can be in a different direction, such as along-X, but the important thing to keep in mind is that there is only a single direction of tension/compression type constraint. The constraint point in the shaft mounting type hoist design is otherwise free to move relative to the backbone.
In the shaft mounting type hoist design, the pillow block bearings (see DEFINITIONS section) each place the following degrees of freedom/constraint on shaft 208: (i) fixed in along X; (ii) free in rotation about X; (iii) fixed in along Y; (iv) free in rotation about Y; (v) fixed in along Z; and (vi) free in rotation about Z. preferably bearings 212 and 214 are “rigid bearings” (see DEFINITIONS section).
Because of the above-identified distribution of degrees of freedom/constraint in the reducer constraint point and on shaft at the locations of the pillow bearings, the shaft mounting type hoist system 200 is free to move so it can accommodate some shaft bending (see FIG. 1 at axis A2) and/or some imprecision in the coaxial alignment of the bearings 212, 214, 224, 228. This accommodation makes shaft mounting an advantageous type of design from a kinematic perspective.
Another conventional hoist system is shown in U.S. Pat. No. 4,796,862 (“Peppel”). The Peppel winch includes a pillow block bearing 30 which allows the shaft some degree of freedom of motion with respect to its axis. This is another way to reduce the requisite degree of rigidity and precision of components when making and assembling a hoist.
Other publications which may be of interest may include the following: (i) pillow bock bearing Wikipedia entry (http://e.wikipedia.org/wiki/Pillow_block_bearing as of May 5, 2009); (ii) U.S. Pat. No. 6,089,547 (“Juelich”); and/or (iii) U.S. Pat. No. 5,921,529 (“Wilson”).
Description of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section, these discussions should not be taken as an admission that the discussed publications (for example, published patents) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Description of the Related Art Section, they are all hereby incorporated by reference into this document in their respective entirety(ies).